A power generating wind turbine comprises a nacelle installed on a tower, a wind turbine rotating blade, a gear-box inputted with a wind force received by the wind turbine rotating blade via a main shaft and a generator driven by an output of the gear-box. Such power generating wind turbine is known, for example, by Patent Documents 1 to 3 as mentioned below.
In the Patent Document 1, for example, a power generating wind turbine is disclosed having a structure in which a rotor provided with a wind turbine rotating blade is directly installed on a planetary carrier of a gear-box to be supported to the gear-box.
Also, in the Patent Document 2, a power generating wind turbine is disclosed having a structure in which a rotor hub is directly installed on a planetary holder to be supported to a gear-box.
Further, in the Patent Document 3, a power generating wind turbine is disclosed having a structure in which a rotor is assembled into a gear-box to be supported to the gear-box. An annular gear carrier and an annular gear of the gear-box are directly fitted to this rotor so that the rotor itself constitutes a portion of the gear-box.                Patent Document 1: European laid-open patent application No. 0811764 (3rd Column and FIG. 1)        Patent Document 2: World laid-open patent application No. 02/079644 (4th Column and FIG. 2)        Patent Document 3: US laid-open patent application No. 2002/0049108 (Abstract and Figures)        
In the prior art power generating wind turbines, however, there are shortcomings as follows: That is, the construction is made such that the wind turbine rotating blade and the rotor are supported to the gear-box and hence the gear-box and the gear-box supporting members are required to have a sufficient strength to withstand a load added to the rotor, such as a radial load, thrust load and bending load.
The size of the gear-box is decided depending not only on its speed-up ratio but also on its required strength. That is, even if a speed-up ratio is the same, a gear-box for which a higher strength is required is inevitably made larger to that extent. For this reason, the power generating wind turbines disclosed in the Patent Documents 1 to 3 need to be provided with a large size gear-box.
Such a large size gear-box has a heavy weight and hence the load adding to the gear-box, nacelle and tower supporting the nacelle also becomes large. Thus, these parts and components are required to have a higher strength, and this results in these parts and components having a large size and heavy weight.
In the prior art power generating wind turbine, therefore, there are problems not only in the manufacturing cost but also in the transportation and installation work of each of the constructional parts and components, such as the gear-box, nacelle, tower or the like.
Moreover, by using such a large size gear-box, a space in the nacelle becomes narrower and the freedom of structure of the nacelle and the freedom of arrangement of the parts and components installed in the nacelle become smaller so that the design becomes difficult.
Also, in such construction of the rotor being supported to the gear-box, if the gear-box is to be overhauled for maintenance, the rotor must be once taken out of the gear-box and placed on the ground. Thus, the maintenance work becomes very troublesome.